I'll first let you know to keep in mind that you can undelete (your own) questions freely.
As for your main question, there is a set of criteria for keeping reputation on a deleted question (or answer), which can also be found here:
- The post must be at least 60 days old.
- You must have earned a net score of +3 or higher to keep the reputation.
So, if you have only one upvote on a question, you would lose that reputation.
To be frank, though, a single +5 isn't worth worrying over if you think the question isn't a good one to keep around. On the other hand, if you simply already know the answer, you could post an answer yourself. (See: When to delete your own question)